Parallels Desktop allows you to run XP/Vista in a virtual machine on you Intel Mac.
I installed it on my MacBook basically because I've used Paint Shop Pro so much and have a big collection of .psp images that I don't want to convert.
Flawless install of XP and runs like a charm - you'd never know it was in a VM. Quick too.
I did bump up the Mac's memory to 2GB though, just on general principles.
